Ferrous alloys for high temperature use



Patented Dec. 16, 1947 FERROUS ALLOYS F TURE R HIGH TEMPERA- USE Russell Franks and William 0. Binder. Niagara Falls, N. Y.. assignors, by mesne assignments, to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Application June 13, 1945, Serial No. 599,309

9 Claims. (Cl. 75-128) This invention relates to ferrous alloys for use at high temperatures, referring more particularly to alloys suitable for use in applications where great strength at high temperatures is req uirech,

The trend of modern engineering is toward the utilization of high temperatures for many and diverse operations. For example, chemical processes are today conducted at very high temperatures, a notable instance being petroleum refining. Also, the quest for improved power sources had led to the investigation and developmentof such devices as superchargers, gas turbines. jet propulsion apparatus and the like all operating at high temperatures. These developments demand of the metallurgist metals and alloys which will withstand prolonged exposure to temperatures well above about 700 F. and in many instances well above about 1200 F. The problem is complicated by the fact that severe mechanical stress is often encountered at these temperatures.

For parts of such devices as superchargers, gas turbines, jet propulsion apparatus and the like, it is necessary to employ alloys that are capable of withstanding severe mechanical stress at high temperatures. Depending upon the design and the intended use of such devices, the temperature ranges at which they operate may be separated into a range between 900 F. and about 1200 F. and into a range upwards of 1200 F. Associated parts and apparatus may be required to withstand temperatures of about 700F. and above. In devices operating within the lower temperature range, generally much higher stresses are applied than in devices operating above 1200 F. In many instances it is desired that alloys for use in such apparatus be capable of being hot-worked and machined, while in other instances the alloys may be employed in the form of castings. In any event, the alloys must have high strength.

A number of alloys have been proposed for use at high temperatures, but the utility of these alloys has been limited either because they are not hot-workable or machinable, or because they become brittle upon prolonged exposure to high temperatures. One of the characteristics of highly alloyed ferrous materials is that as the ferrous solid solution alloy contains more and moreof the alloying metals to increase high tempera ure strength, the stability of the materials at high temperatures tends to decrease so that on prolonged exposure to high temperature the materials become excessively brittle.

It is the principal object of this invention to provide ferrous alloys suitable for use in applications where temperatures above about 700 F. are normally encountered. A further object is the provision of hot-workable and machinable ferrous alloys for use at such elevated temperatures. Another object is the provision of ferrous alloys capable of withstanding severe mechanical stress at elevated temperatures above about 700 F. A more specific object is the provision of ferrous alloys and articles wrought or cast therefrom capable of withstanding severe mechanical stress at elevated temperatures above about 1200 F. up to about 1500 F,

The invention by means of which these objects are achieved is based on the discovery that the addition of small, properly-proportioned quantitles of molybdenum, tungsten, at least one element selected from the group consisting of columbium, tantalum, tatanium, and vanadium and at least one element selected from the group consisting of aluminum and boron to iron-chromiumnickel alloys produces a remarkable increase in the high temperature strength of such alloys without detrimentally affecting their high temperature stability.

The invention comprises ferrous alloys containing 10% to 30% chromium, 2% to 40% nickel, 0.5% to 7.5% molybdenum, 0.5% to 10% tungsten, 0.5% to 5% in the aggregate of at least one metal selected from the group consisting of columbium, tantalum, titanium, and vanadium, and 0.1% to 3% in the aggregate of at least one metal selected from the group consisting of aluminum and boron, the boron content not exceeding 0.7%, and the aluminum content being not less than 0.5% in the absence of boron, the remainder of the alloys being iron except for incidental impurities and small quantities of elements customarily present in steels of good quality. Generally preferred ranges for molybdenum and tungsten are 1% to 5% molybdenum and 0.5% to 5% tungsten. No more than 2% each ,of titanium and vanadium should be present in the alloys.

Carbon is always present in the alloys of the invention. Preferably it does not exceed about 1%, and if hot working of the alloys is desired, the maximum carbon content should be 0.35%. Nitrogen is importantly beneficial and is preferably present in a proportion up to 0.25%. .Silicon and manganese may be present, the silicon content preferably not exceeding 1% and the manganese content not exceeding 2% if hot working is desired.

A useful test for determining the suitability of mater als tor use at high temperatures is the socelled stress-rupture test. in this test severel -t' of en alloy to m tested are maintained at a given temperature, each sample being sublooted to s diflerent measured stress. The time required to cause failure of the samples under these conditions of temperature and stress is determined. end the time end stress values obtained are plotted to yield a. curve tor the particular materiel under test. From this curve can be determined the stress the material will withstand for e given period of time, soy 1,000 hours. at the particular temperature ior which the curve was drawn. This test provides a. convenient method of determining the iced carrying ability of a material. It elso gives some indication of whether or not the meterial becomes embrittled upon pro longed exposure at the temperature of the test. A brittle materiel will bresls without elongation, whereas ductile material will elongate before failure. I

tressrupture tests conducted in the manner just described indicate that the alloys oi the invention nieintsin great strength at temperatures es high. as 1500 F. and that even at such high temperature the alloys possess good ductility.

Typical examples of the improvement in high temperature strength of chromium-nickel steels imported by the addition of molyenum, tungsten, columhluin, titanium, and boron in various cobinetions are indicated by the date. in Table 1 below. in this table are reported the results of stress-rupture tests in which 9. stress of 20,000 pounds per square inch eves applied to ssample oi the steel (in the as-iorged condition) to be.

tested while the sample was maintained at a tem pereture oi l500 F. The time in hours required tor the sample to fail under these extremely severe conditions is given in the table.

mental effect on hot-workability and tseldsbility, particularly the latter property. Alloys within the composition limits defined may be welded readily by any of the common welding methods. ior euample, electric arc, oxyacetylene, submerged=meit electric welding, or solid-phase pressure welding, sound, strong and tough welds being produced without undue embrittlement of weld metal or base metal, and such welds retain their toughness at elevated temperatures. However, ii too high a proportion of any oi these elements is present in the alloys, welds produced usually sufier from loss of toughness at elevated temperatures.

The presence 03 nitrogen in the alloys of the invention within the range indicated is important, nitrogen having a beneficial efiect on the high temperature stability of the alloys.

Being hot-workable, machinehle, weldable, and castable, and possessing remarkable strength at elevated temperstures up to about l500 1 the alloys of the invention are particularly well suited to use in the fabrication oi articles such as parts of superchargers, gas turbines, jet propulsion apperatus and the like which are required to withstand severe mechanical stress at elevated tem-= peratiu'es. ".iheir freedom from embrittlement upon prolonged exposure at high temperatures recoends their use where dependability of operation is essential.

Related subject matter is disclosed and claimed in our copending application Ser. No. 590,308, filed June 13, 1945.

We claim:

v 1. An alloy containing about to chromium; 2% to nickel; 0.5% to 7.5% molybdenum; 0.5% to 10% tungsten; an aggregate of 0.5% to 5% of at least one metal selected from the group consisting of columbi, tantalum,

Tome Coznpceition; hanieindsr Substantially all Fe Hours %O1? %Ni %M0%W %Gb %n %o 9.31s %Other is. s s 5 Nil Nil Nil Nil c 01 0. 0:. Nil. 7 0.10 19 o 1.8 1. s o. 54 0. 61 o. 05 0. 01 0.1 'r 55. a 19 9 i. 5 l. 8 Nil 0. 7 0. 07 D. 04 0.2 T 95. 5 18.5 e 1.25 -1. 4 Nil 0. 4 on 0.04 0.3 T 95 18. 5 9 1. 25 1. 4 0. 5 0. 4 0. 08 0. 04 0.3 T

The date. in the above table demonstrate the remarkable improvement in high temperature strength of a steel containing about 19% chromium and 9% nickel imported by the addition of small quantities of molybdenum. tungsten, coluxnbium, and titanium. From a life of six utes st l500 F. under stress of 20,000 pounds per square inch the life of the steel was raised to nearly 100 hours by the addition of these elements.

In manufacturing the alloys of this invention care should be taken that the composition limits set forth be closely adhered to with regard to the intended use of the alloys since material variations in the. proportions of the several ingredients detrimentelly sheet the desired properties. so: esple, if the alloys are to be employed as castlogs, the carbon content may be as high as 1%; out if hot-workability is. desired, the carbon content should be kept at a. maximum of about 0.35%

and preferably should notexceed 0.2%.

similarly, the proportions of molybdenum, tungsten, columbium, tantalum, titanium, vanadiu'm, aluminum, and boron present in the alloys nflect hot-workability'and weldability. Too high a proportionof any of these elements 118,8 0 detrigate of 0.1% to 3% of at least one metal selected from the group consisting of aluminum and boron. the boron content not exceeding 0.7%, end the aluminum content being not less than 0.5% in the absence oiboron; the remainder substantially ell iron and incidental impurities.

2. An alloy containing about 10% to 30% chromium; 2% to 40% nickel; 1% to 5% molybdenum; 0.5% to 5% tungsten; an aggregate of 0.5% to 5% of at least one metal selected from the group consisting of columbium. tantalum, titanium, and vanadium, the titanium and vanadium contents each not exceeding 2%; nitrogen in an effective proportion up to 0.25%: an aggregate of 0.1% to 3% of at least one metal selected from the group consisting of aluminum and boron, the boron content not exceeding 0.7%. and the aluminum content bein mt less than-0.5% in the absence of boron; the remainder substantially all iron and incidental impurities.

3. Analloy containing about 10% to 30% chromium;-2% to 40% nickel; 1% to 5% molybdenum; 0.5% to 5% tungsten; an aggregate of 0.5% to 5% of at least one metal selected from the group consisting of columbium, tantalum, titanium, and vanadium, the titanium and vanadium contents each not exceeding 2%; nitrogen in an effective proportion up to 0.25%; an aggregate of 0.1% to 3% of at least one metal selected from the group consisting of aluminum and boron, the boron content not exceeding 0.7%, and the aluminum content being not less than 0.5% in the absence of boron; carbon in an effective proportion not exceeding 1%, the remainder substantially all iron and incidental impurities.

4. A hot-workable alloy containing about to 30% chromium; 2% to 40% nickel; 1% to 5% molybdenum; 0.5% to 5% tungsten; an aggregate of 0.5% to 5% of at least one metal selected from the group consisting of columbium, tantalum, titanium, and vanadium, the titanium and vanadium contents each not exceeding 2%; nitrogen in an eifective proportion up to 0.25%; an aggregate of 0.1% to 3% of at least one metal selected from the group consisting of aluminum and boron, the boron content not exceeding 0.7%. and the aluminum content being not less than 0.5% in the absence of boron; carbon in an effective proportion not exceeding 0.35%, the remainder substantially all iron and incidental imto 7.5% molybdenum; 0.5% to 10% tungsten; an

aggregate of 0.5% to 5% of at least one metal selected from the group consisting of columbium,

tantalum, titanium, and vanadium, the titanium and vanadium contents each not exceeding 2%; nitrogen in an effective proportion up to 0.25%; an aggregate of 0.1% to 3% of at least one metal selected from the group consisting of aluminum and boron, the boron content not exceeding 0.7%, and the aluminum content being not less than 0.5% in the absence of boron; the remainder substantially all iron and incidental impurities.

S. A cast article which in its normal use is required to withstand mechanical stress at elevated temperatures not exceeding about 1500 F., which article is composed of an alloy containing about 10% to 30% chromium; 2% to 40% nickel; 0.5% to 7.5% molybdenum; 0.5% to 10% tungsten; 0.5% to 5% columbium; 0.1% to 0.7% boron; manganese in an effective proportion up to 2%; silicon in an effective proportionto 1%; nitrogen in an effective proportion up to'0.25%; carbon in an effective proportion not exceeding 1%; remainder substantially all iron.

7. A wrought article which in its normal use is required to withstand mechanical stress at elevated temperatures up to about 1500 R, which article is composed of an alloy containing about 10% to 30% chromium; 2% to 40% nickel; 0.5% to 7.5% molybdenum; 0.5% to 10% tungsten; an aggregate of 0.5% to 5% of at least one metal selected from the group consisting of columbium, tantalum, titanium, and vanadium, the titanium and vanadium contents each not exceeding 2%; nitrogen in an effective proportion up to 0.25%; an aggregate of 0.1% to 3% of at least one metal selected from the group consisting of aluminum and boron, the boron content not exceeding 0.7%, and the aluminum content being not less than 0.5% in the absence of boron; the remainder substantially all iron and incidental impurities.

8. A wrought article which in its normal use is required to withstand mechanical stress at elevated temperatures not exceeding about 1500 R, which article is composed of an alloy contain ing about 10% to 30% chromium; 2% to 40% nickel; 0.5% to 7.5% molybdenum; 0.5% to 10% tungsten; 0.5% to 5% columbium; 0.1% to 0.7% boron; manganese in an effective proportion up to 2%; silicon in an effective proportion up to 1%; nitrogen in an effective proportion up to 0.25% carbon in an effective proportion not exceeding 0.35%; remainder substantially all iron.

9. A welded article which in its normal use is required to withstand mechanical stress at elevated temperatures not exceeding about 1500 F., which article is composed of an alloy containing about 10% to 30% chromium; 2% to 40% nickel; 0.5% to 7.5% molybdenum; 0.5% to 10% tungsten; 0.5% to 5% columbium; 0.1% to 0.7% boron; manganese in an effective proportion up to 2%; silicon in aneffective proportion up to 1%; nitrogen in an effective proportion up to 0.25%; carbon in an effective proportion not exceeding 0.35%; remainder substantially all iron.

RUSSELL FRANKS. WILLIAM O. BINDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,397,034 Mohling Mar. 19, 1946 2,373,490 Mohling Apr. 10, 1945 2,191,790 Franks Feb. 27, 1940 2,227,065 Charlton Dec. 31, 1940 OTHER REFERENCES Pamphlet by Electro Metallurgical Co. of Union Carbide and Carbon Corp., Nitrogen in Chromium Steels, 1941, New York. (Copy in Div. 3 in -126.)

The Iron Age, Nitrogen in Chrome-Nickel Steels, March 29, 1945, pages 56 to 60. (Copy in Div. 3 in.75-128.) 

